restore notifications api post-merge-rollback
add missing file
add missing files
keep flagged threads and comments out of digest
remove unnecessary methods
add thread subset test
add flagging test to notifications
formatting issues
update tests to manufacture threads and subscriptions
add sleep to prevent tests artificially failing
update tests to manufacture fixtures instead of relying on existing data
fix timing used on tests
Merge pull request #45 from edx/feature/kevin/notifications_restful_take_2

restore notifications api post-merge-rollback